Put an End to Snap, Crackle and Pop

Have you connected a battery, a charge controller or an inverter and had rapidly charging capacitors make a loud pop and maybe even a welding arc that messes up a bolt?

That can be really annoying and it can be dangerous, too. I have never had it blow up a battery but I have had it mess up threads on a battery terminal. The large capacitor bank in my inverter always makes an unnerving POP! Recently, after the inverter suffered a dead short, replacing the fuse made a KABOOM! that could have damaged a finger if it had been in the wrong place. It didn’t do my nerves any good.

As I undertook to test and repair the inverter I was a little gun shy. I didn’t want to blow up a new set of transistors in case they were not the only issues and I did not want to cause further damage to the circuit board. What to do?

Sometimes you just have to stare at a problem and maybe talk it over with your accomplices and acquaintances. One such collaborator is Bruce (in Pa.) (We call him that because he is Bruce and he is in Pennsylvania.) The answer seems to be a precharge resistor and you probably already have one.

I should have thought of this earlier because my golf cars, which control some serious amounts of power–600 amps at 48 V– use them. The precharge resistor can not only take the pop out of connecting capacitive loads, it can warn of impending doom if, say, your inverter has a dead short.

Here’s what I did. I found a light socket and a 40 watt incandescent light bulb, a couple of pieces of wire and some gator clips. If you have an old desk lamp, you can use that, just make sure the bulb is the old-timey one and not a CF or LED. I would go with a bulb in the 20-40 watt range. If I need to start up the inverter after being offline (I just re-installed the repaired 10kw module) I clip the light across the empty fuse holder. The bulb glows briefly as the capacitors charge. Then I can slip in the fuse, snug it down and remove the lamp.

No snap, crackle or pop. If the power module repair had not gone well, the bulb would have continued to glow instead of going dark. We would have eliminated the KABOOM!

That’s a big help from something you might already have in your junk closet.